LMWHs are the mainstay for primary and secondary VTE prevention. Although clinical practice guidelines do not distinguish between agents, current evidence suggests that tinzaparin is the safest alternative for both prophylaxis and treatment of VTE in special populations, such as pregnant women, cancer patients and patients with renal impairment.
Several retrospective studies in pregnant women have documented bleeding rates ranging from 9.7–10.3%, with major bleeding events appearing rarely [10–12]. Interestingly, in the study of Shaaban et al. that only included patients with recurrent miscarriages, bleeding rates were equal to zero [13]. Furthermore, early tinzaparin administration resulted in significantly decreased miscarriage (< 20 weeks; 23.6% versus 48.9%, P = .002) and fetal death rates (> 20 weeks; 13.7% versus 27.5%, P = .031) and finally, significantly increased take-home baby rates (65.7% versus 36.2%, P = .001). Preclinical data have also supported the use of LMWHs in women with unexplained recurrent pregnancy loss by the upregulation of CXCL10 and CXCL11 and the induction of Th1 response early in pregnancy [26].
Lately, direct oral anticoagulants (DOACs; edoxaban and rivaroxaban) have been approved as an alternative to LMWHs for the treatment of acute VTE in patients with cancer, not only because of the clinically acceptable results but also because of the discomfort and cost associated with the use of the latter [27–29]. Also, apixaban has proved noninferior to the LMWH dalteparin for the treatment of acute VTE in patients with cancer (HR, 0.63; 95% CI, 0.37 to 1.07; P < .001 for noninferiority); patients with acute myeloid leukemia and those with primary brain tumors or brain metastases were excluded from this trial [30]. DOAC use in patients with cancer should be applied with caution. LMWHs are still preferred for cancer patients in whom drug-to-drug interaction is a concern; depending on the specific agent that was studied, trials often excluded patients receiving strong inducers or inhibitors of P-glycoprotein or CYP3A4. Additionally, interaction of DOACs with newer cancer therapies remains yet to be determined as most clinical trials included only few patients receiving immune checkpoint inhibitors. Furthermore, LMWHs remain the preferred agents for cancer patients who have undergone surgery involving the upper gastrointestinal tract because absorption of DOACs occurs in the stomach or proximal small bowel. Last but not least, practicing physicians have accumulated years of clinical experience with LMWH use in special circumstances such as thrombocytopenia, VTE recurrence, bleeding events and tumors of the central nervous system. As far as tinzaparin use is concerned, different prospective clinical trials have reported rates of major bleeding varying from 0.8–7% [14–17].
Tinzaparin sodium can be safely administered in patients with renal impairment and CrCl > 20 ml/min. Furthermore, data from recent pharmacokinetic studies showed that repeated prophylactic and therapeutic doses of tinzaparin do not bioaccumulate, vindicating its use without dose adjustment even in patients with severe renal impairment and CrCl < 20 ml/min [20, 22]. The elimination of tinzaparin, resembles that of unfractionated heparin (UFH), being mediated by two systems that act in succession: cellular uptake (reticuloendothelial cells) via hyaluronic acid receptor for endocytosis receptors that is activated at low-dose range and is saturable and renal excretion via renal tubules that is takes over as doses increase and is non-saturable. The above concept exhibits molecular weight (MW) dependency. Thus, LMWHs with a MW below approximately 5000 Da are predominantly excreted by the kidney, in a dose- independent manner. On the contrary, tinzaparin (6500 Da) and to a lesser extent dalteparin (5700 Da) employ first-order pharmacokinetics, with the alternating involvement of cellular and renal routes of elimination.
In the era of personalized medicine, where treatment paradigms are relentlessly shifting, tinzaparin sodium is a safe alternative for populations that carry increased risk for both thrombosis and bleeding. Head-to-head clinical trials are required to assess whether tinzaparin is safer than other anticoagulants, including other LMWHs and DOACs, for pregnant women with unexplained recurrent pregnancy loss, cancer patients and patients with severe renal impairment and CrCl < 20 ml/min.